1. Field of the Invention
The present invention relates to an armature having an armature winding with four parallel circuits, which is applied to a rotating electrical machine having 84 three-phase two-pole slots.
2. Description of the Related Art
In a large-capacity rotating electrical machine, an armature winding is provided in two layers in slots with upper coil pieces and lower coil pieces provided in a laminated core, and the two layers of armature winding are connected in series to provide a high voltage, thereby increasing an apparatus capacity. However, as an armature winding rises in voltage, the thickness of a main insulator of the armature winding needs to be increased to withstand the voltage. As a result, the cross-sectional area of a conductor of the armature winding is decreased. This increases a current density and loss.
Particularly, in a machine adopting indirect cooling system for cooling an armature winding from the outside of a main insulator, a thick main insulator increases thermal resistance and temperature of an armature winding. Therefore, an armature winding is divided into two or more parallel circuits to decrease in voltage and main insulator thickness, while keeping an apparatus capacity, thereby increasing a cooling capacity with decreased loss. Particularly, in an indirect cooling large-capacity machine, it is common to increase the number of slots to increase the peripheral length of an armature winding to be cooled. Therefore, it is necessary to use an armature winding having three or more parallel circuits.
However, if a two-pole machine adopts an armature winding with three or more parallel circuits, it is impossible to generate the same voltage in parallel circuits. Therefore, a circulating current occurs generated among the parallel circuits, and increases loss in the armature winding.
To decrease the loss caused by the circulating current, it is necessary to minimize the imbalance among the voltages generated in the parallel circuits. It is thus necessary to give special consideration to arrangement of coil pieces in each parallel circuit in each phase belt.
A phase belt mentioned here means a winding part, which forms the same phase by dividing each of three phases into a plurality of parts, housing upper and lower coil pieces in two layers into slots provided in an assigned armature core, and sequentially connecting them in series.
An explanation will be given of an example of improvement in arrangement of coil pieces by referring to a developed perspective view showing an armature winding in FIG. 7, showing a part for one phase. FIG. 7 is a developed perspective view showing one phase of an example of an armature winding having four parallel circuits applicable to a rotating electrical machine having 72 three-phase two-pole slots, based on U.S. Pat. No. 2,778,962 (hereinafter, called a Taylor patent).
FIG. 7 shows a part for only one phase. It is however appreciated that parts for the other two phases are obtained by displacing the configuration of the armature winding of FIG. 7 by 120° and 240° (electric angle), respectively, and an illustration thereof is omitted.
As shown in FIG. 7, an armature 11 comprises an armature core 12, and an armature winding 14 housed in slots 13 provided in the armature core 12.
In the armature winding 14, when parallel circuits housed in the slots 13 are indicated by parenthetic numbers 1, 2, 3 and 4, twelve upper coil pieces 15a and lower coil pieces 16a, forming a first phase belt 17, are numbered 1, 2, 2, 1, 2, 1, 1, 2, 1, 2, 2 and 1 sequentially from a pole center Pa, and twelve upper coil pieces 15b and lower coil pieces 16b, forming a second phase belt 18, are numbered 3, 4, 4, 3, 4, 3, 3, 4, 3, 4, 4 and 3 sequentially from a pole center Pb, thereby decreasing a voltage deviation (an absolute value of deviation from an average phase voltage) in the parallel circuits and a phase difference deviation circuits (a phase angle deviation from an average phase voltage) in the parallel circuits.
To realize the above connection, in the armature winding 14 of FIG. 7, coil ends 19a on the connection side are connected by fourteen jumper wires 20a, coil ends 19b on the counter-connection side are directly connected, and lead-out ends of corresponding parallel circuits are connected between the first and second phase belts 17 and 18, by connection conductors 21.
As an example concerning the deviation of voltage and phase angle in parallel circuits, there is a U.S. Pat. No. 2,778,963 (hereinafter, called a Habermann patent). This patent indicates that a reference value of voltage deviation is 0.4% or lower, and a reference value of phase angle deviation is 0.15° or lower. However, in the Taylor patent mentioned above, the voltage deviation is 0.12% and the phase angle deviation is 0° in the parallel circuits, which are highly balanced compared with the above reference values, and sufficiently effective in decreasing a circulating current.
In the connection method disclosed in the Taylor patent, the deviation of voltage generated in each parallel circuit is reduced to small, and this method is suitable from an electrical viewpoint, but its application is limited to a rotating electrical machine having 72 three-phase two-pole slots.
An armature winding having four parallel circuits is mechanically complex. Namely, as shown in FIG. 7, for making an armature winding, it is necessary to provide fourteen jumper wires 20a per phase at the connection-side coil end 19a, for connecting upper coil pieces 15 and lower coil pieces 16. Connection of the jumper wires 20a requires much time and labor, and it is important to ensure the insulation and fixing strength of the jumper wires 20a. 
There are twenty locations per phase for connecting the upper and lower coil pieces 15 and 16, except a location to connect a lead-out connection conductor 21, at the connection-side coil end 19a. At fourteen locations per phase among these twenty locations, the connection side jumper wires 20a are connected in a short distance, the jumper wire connection work is uneasy, and it is difficult to ensure the insulation and fixing strength of the jumper wire, due to the interference between the jumper wires 20a, and between the jumper wires 20a and lead-out connection conductors 21.